1. Field of the Invention
The present invention generally relates to excimer lamps, and more particularly, to excimer
lamps having a discharge vessel made of silica glass, wherein an ultraviolet reflection film is formed on the surface facing a discharge space of the discharge vessel.
2. Description of Related Art
Various technologies for cleaning treatment, film forming treatment, and ashing treatment, and the like, have been developed and put into practical use recently for treating the surface of an article to be treated made of metal glass or other materials by means of action of vacuum ultraviolet radiation irradiated onto the article to be treated and the ozone generated by the vacuum ultraviolet radiation. The ultraviolet radiation is not longer than 200 nm in wavelength.
A device for emitting vacuum ultraviolet radiation typically is equipped with an excimer lamp as a light source in order to form excimer molecules by means of excimer discharge and with light being emitted from the excimer molecules. Many experiments have been attempted in order to enhance the intensity of the radiated ultraviolet radiation with more efficiency from such excimer lamps.
As shown in FIGS. 6(a) & 6(b), an excimer lamp 50 includes a discharge vessel made of silica glass, which allows passage of ultraviolet radiation, wherein electrodes 55, 56 are provided on the inner side and outer side of the discharge vessel 51 and ultraviolet reflection films are formed on the surfaces exposed to a discharge space S of the discharge vessel 51. Some technologies have been disclosed to form an ultraviolet reflection film using ultraviolet scattering particles having a high ultraviolet reflectivity, such as silica, aluminum oxide (alumina), magnesium fluoride, calcium fluoride, lithium fluoride and magnesium oxide, for example, as described in JP 3580233 B2. Such an excimer lamp is provided on part of the discharge vessel 51 with a light exit part 58 from which ultraviolet radiation generated in the discharge space S can exit because the ultraviolet reflection film 20 is not formed on that portion.
In the excimer lamp 50 having the aforementioned configuration, ultraviolet radiation generated inside the discharge space to be incident on an ultraviolet reflection film is diffused and reflected (e.g., refraction and reflection are repeated on the surface of multiple ultraviolet scattering particles) and then exited from a light exit part 58. However, in the excimer lamp including an ultraviolet reflection film having the aforementioned configuration, the ultraviolet reflection film is of an appropriate thickness in order to prevent ultraviolet radiation incident on the ultraviolet reflection film to pass through the ultraviolet reflection film, thus preventing a decline in the reflectivity of ultraviolet radiation